The invention relates to the use copper (I) complexes of formula (I), wherein X is nitrogen or a C-R group, R is alkyl or aryl and Ar is Phenyl or Naphthyl, each of which is optionally alkoxy, alkylthio, alkylamino, dialkylamino, alkoxycarbonyl, alkoxysulfonyl, halogen, cyano, carboxyl, hydroxysulfonyl or nitro substituted, wherein two optionally substituted phenyl- or naphthyl rests are interconnected by a simple chemical connection via carbon atoms situated in α- and α' with respect to a phosphor atom, n represent values equal to 1, 2 or 3, and Y is a halogen, cyano, thiocyanato, alkoxy, aryloxy, alkylthio, arylthio, alkylamino, dialkylamino, arylamino or diarylamino. The invention also relates to electroluminescent layers containing at least one copper (I) complex of formula (I), OLEDs containing at least one copper (I) complex of formula (I) or the inventive electroluminescent layer and stationary screens containing the incentive OLEDs. Said invention also relates to novel copper (I) complexes of formula (Ia) and (Ib), wherein R, Ar and n have the same designations as specified in formula (I), in formula (Ia) Y is cyano, thiocyanato, alkoxy, aryloxy, alkylthio, arylthio, alkylamino, dialkylamino, arylamino or diarylamino and in formula (Ib) Y is halogen, cyano, thiocyanato, alkoxy, aryloxy, alkylthio, arylthio, alkylamino, dialkylamino, arylamino or diarylamino. Said invention is used for organic electroluminescent diodes.